All publications mentioned throughout this application are fully incorporated herein by reference, including all references cited therein.
Asthma is a chronic and complex inflammatory disease of the airways characterized by airflow obstruction, bronchial hyper-responsiveness (BHR) and airway inflammation. It is the most common chronic illness of childhood, with up to 20% of children affected in some Western countries. The incidence as well as the number of hospital admissions attributable to asthma continues to rise in both adults and children. Over the last decade the importance of airway inflammation in the disease process has been carefully investigated, and revealed that the asthmatic tissue is characterized by the accumulation of a large number of inflammatory cells (e.g. eosinophils, neutrophils, basophils, mast cells), increased mucus production, epithelial shedding and hypertrophy, mucus, smooth muscle cell hypertrophy and sub-mucosal mucus glands hyperplasia/metaplasia and fibrosis. Notably, chronic inflammation of the asthmatic lung leads to structural changes, that in turn exacerbate the hyperresponsiveness observed in this disease. While these findings have provided the rationale for the development of multiple therapeutic agents that interfere with specific inflammatory pathways, the development of the asthma phenotype is likely to be related to a complex interplay of a large number of genes combined with environmental factors. Recent genome searches have revealed that at least 19 genes contribute to asthma susceptibility and microarray studies of asthmatic tissue revealed the involvement of hundreds of genes. Moreover, microarray analysis has recently demonstrated increased expression of 291 genes that were commonly involved in murine disease pathogenesis rather than to a particular mode of disease induction [Zimmermann, N. et al. (2003) J. Clin. Invest. 111: 1863-74]. Therefore, a central issue still under pursuit is identification of fundamental molecules/pathways that govern the processes underlying inflammation in asthma. Nonetheless, no asthma drug so far has been able to inhibit the initial steps of the signaling cascade of this agonizing medical condition. Therapeutic drugs for asthma are usually directed to the symptoms, i.e., ex post facto of the asthma attack.
Eosinophils are thought to be key effector cells in asthma by the release of basic granule proteins, membrane phospholipid metabolites and a variety of cytokines. For example, the eosinophil basic proteins have been found to be highly toxic in vitro to respiratory epithelial cells, at concentrations detected in biological fluid from patients with asthma. Furthermore, eosinophils produce matrix metalloproteinase (MMP)-9, tissue inhibitor of matrix metalloproteinase (TIMP)-½, contain heparanase and are a source for vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF) and b-fibroblast growth factor (b-FGF), indicating their role in asthma-associated symptoms.
Since a central question concerning eosinophils is to understand the mechanisms by which these cells get activated or inhibited and whether a “disease-specific” activator exists, the inventors screened eosinophils with monoclonal antibodies (mAbs) produced to recognize epitopes expressed on T lymphocytes and NK cells, preferably. The inventors found that human eosinophils express 2B4 [Munitz, A. et al. (2005) J. Immunol. 174: 110-118], and that 2B4 is a functional activator receptor on these cells in vitro, suggesting that a complex network of activating signals regulate the immunological or inflammatory responses coordinated by eosinophils.
CD48 is a glycosyl-phosphatidyl-inositol (GPI) anchored protein belonging to the CD2-subfamily, which is involved in lymphocyte adhesion, activation and co-stimulation. It is expressed mainly on hematopoietic cells and exists in both a membrane-associated and a soluble form. Studies on CD48-deficient mice indicate that CD48 has a broad immunological importance. In fact, CD48 has been described to interact with extracellular matrix components such as heparin sulfate, facilitate cell adhesion, innate responses to bacterial infection and graft rejection and provide co-stimulatory signals to T and B lymphocytes. Furthermore, CD48 has a distinctive role in orchestrating mast cell innate responses towards E. coli. Besides, CD48 is a low affinity ligand for CD2 but a high affinity ligand for 2B4 [Brown, M. H. et al. (1998) J. Exp. Med. 188(11):2083-90]. CD48-2B4 interactions can modulate T cell, B cell and NK cell functions and cross-talk. Studies with 2B4 gene-targeted mice, demonstrated that 2B4-CD48 interactions are essential for expansion and activation of murine NK cells. The absence of functional 2B4-CD48 interactions impairs NK cell cytotoxic response and IFN-γ release upon tumor target exposure. Furthermore, activated NK cells significantly increase the CD3-dependent proliferation of CD8+ and CD4+ T cells by a 2B4-CD48 dependent mechanism. n. Furthermore, cross-linking of CD48 on the surface of rodent T lymphocytes induced mobilization of the intracellular calcium inositol triphosphate concentration. T cell activation via CD48 combined with CD3 induced enhanced IL-2 release, T cell receptor signaling and cytoskeletal reorganization. Furthermore, cross-linking of CD48 on the surface of rat or murine B cells induced strong homotypic adhesion suggesting that this molecule can be involved in B cell activation. In humans, cross-linking of CD48 on purified tonsillar B cells significantly increased CD40-mediated activation. Additionally, CD48, in combination with IL-4 and/or IL-10 is able to induce B cell aggregation, proliferation and IgG secretion [Klyushnenkova, E. N. et al. (1996) Cell Immunol. 174(1):90-8].